This invention relates to a structural element of an aircraft having a hollow part and an indicator of formation of ice in such hollow part.
The outer surfaces of an aircraft (whether, for example, on the fuselage or the wing group) generally are formed by a relatively thin skin, which therefore is stiffened in standard manner by structural elements, such as frames and stringers, for example.
In order to play their mechanical part correctly without excessive contribution of weight, these structural elements frequently have shapes that define a hollow part within the structural element, such as the commonly used omega stringers.
Such hollow parts then may form an inopportune container for liquids, typically condensation and runoff water, in particular for structural elements located at a low point of the part (for example of the fuselage) concerned.
This presence of water proves to be problematic when the temperatures encountered lead to a changeover to the solid state (in practice the formation of ice) which, because of the changes in volume associated with the change of state inside the fixed volume of the structural element, may be accompanied by mechanical stresses detrimental to the mechanical strength of the structural element, by the way, however, with no damage being visible from the outside.
This risk is particularly serious in the case of structural elements made of composite material in which the frost may lead to a separation of the element or to a delamination.
A visual signal of the presence of frost already has been proposed in document FR 2 680 871. This document, however, applies to the general detection of frost on the airplane and therefore in no way considers the possible consequences of frost on the structural elements.